Mucociliary clearance of inhaled particles from the tracheobronchial tree is an important defense mechanism of the lung. Circumstantial evidence indicates that airway secretion of ions, water, and mucus is an important factor in determining the rate of mucociliary clearance. Since the normal and abnormal physiology of these secretory processes is only partially known, my proposal is to study the interrelationships among these processes. Previously, we have shown that there is a predominant chloride ion pump directed toward the tracheal lumen and a lesser sodium ion pump facing in the opposite direction. We performed the initial studies supported by this grant to further characterize this ion transport across the dog tracheal epithelium. These initial studies showed that there was interdependent movement of chloride and sodium toward the tracheal lumen which required both chloride and sodium in the bathing media. Stimulation of ion transport by both acetylcholine and terbutaline required the presence of both chloride and sodium. Additionally, we studied the effects of calcium concentration in the bathing media on the electrical and ion transport properties of dog epithelium. These studies showed that lack of calcium decreased transepithelial electrial resistance. Furthermore, calcium was necessary for the full electrical response to histamine, but was not necessary for responses to acetylcholine or terbutaline. Presently, we are investigating the effect of acetylcholine, terbutaline, histamine and calcium concentration on mucous glycoprotein secretion in dog tracheal epithelium.